Field of the Invention
This invention relates to a process for isolation from solution of partially brominated diphenyl ether mixtures ("Octabrom") having an average of 7.2-8.5 bromine atoms per molecule of diphenyl ether. The isolated Octabrom is crystalline in form, and has a relatively high melting range.
Description of the Prior Art
The flame retardant industry terms and markets mixtures of partially brominated diphenyl ether as "Octabrom". These mixtures, hereafter referred to as Octabrom, are commercially available, typically contain 0-2 weight percent of pentabromodiphenyl ether, 5-15 weight percent of hexabromodiphenyl ether, 40-55 weight percent of heptabromodiphenyl ether, 30-40 weight percent of octabromodiphenyl ether, 5-15 weight percent of nonabromodiphenyl ether, and 0-2 weight percent of decabromodiphenyl ether. The average number of bromine atoms per molecule of brominated diphenyl ether, hereafter referred to as the bromine content, for any particular Octabrom, is dependent on the amounts and the identities of the particular bromo homologs which are present in the Octabrom mixture. The bromine content can be calculated by multiplying the weight percent of each bromo homolog by the number of bromine atoms in that homolog, adding the resulting products and dividing the sum by 100.
Octabrom is a mixture, and therefore does not have a sharp melting point. For purposes herein, the melting point will be expressed as a melting range (M.R.). The melting range can be low, e.g., M.R.=75.degree.-95.degree. C., high, e.g., M.R.=90.degree.-145.degree. C., or can be somewhere in-between, depending on the process and any post-process treatment used in the preparation or production of the Octabrom.
The melting range of any particular Octabrom depends on its amorphous or crystalline nature. The lower melting Octabroms are more amorphous, i.e., much less crystalline, than the higher melting Octabroms which are more crystalline. Another interesting observation is that lower melting Octabroms tend to agglomerate, i.e., tend to form lumps. These lower melting Octabroms can become non free-flowing after being subjected to long storage periods, e.g., a few weeks, and to higher temperatures, e.g., 50.degree.-80.degree. C. during the storage period. Higher melting Octabroms do not have a tendency of agglomeration and are free-flowing.
Apart from the amorphous or crystalline nature of Octabrom and the tendency of agglomeration, Octabrom customers may set melting range as a part of the purchase specifications. Low melt or high melt Octabroms can be required by the Octabrom customers depending on the intended use.
It will be appreciated that there has been a desire to provide Octabroms having a relatively high melting range. Processes have been developed in the prior art for the treatment of slurties of solid Octabrom to increase the melting range. In U.S. Pat. No. 5,000,879, issued to Moore, Jr. et al. on Mar. 19, 1991, there is described a process of forming a slurry of solid Octabrom and a C.sub.1 -C.sub.4 alkanol, maintaining the slurry for a time, generally 1-24 hours, and then separating the treated, solid Octabrom. The Octabrom is washed with water to remove entrained alcohol, and then dried to yield an Octabrom with a higher melting range than the non-treated material. The Moore, Jr. et al. procedure is specifically directed to treating only solid Octabrom, and notes that the low solubility of Octabrom in alkanol is a feature of the process. Similarly, a process for treating solid Octabrom is described in U.S. Pat. No. 5,081,316, issued to Hussain on Jan, 14, 1992, in which the solid Octabrom is slurried in an alkyl halide for a time, and the alkyl halide is then evaporated from the slurry. Hussain requires the use of alkyl halides in which the solid Octabrom is substantially insoluble.